Wear equalizing arrangement for the valve plate of an axial piston machine

ABSTRACT

In an axial piston machine, the rotary control face of the cylinder block slides on the stationary control face of a valve plate which has a pair of part-circular inlet and outlet slots swept by cylinder ports of the cylinder block. Fluid flowing through the slots and leaking between the control faces, contains impurities so that annular sealing face portions of the stationary control face adjacent the slots, tend to be more worn than the annular supporting face portions located radially inward and radially outward of the sealing face portions. Radial grooves, or grooves slanted in the direction of rotation, connect the slots directly with the outer and/or inner supporting face portions so that the impurities produce wear of the supporting face portions, substantially equal to the wear of the sealing face portions, whereby a constant clearance is maintained between the control faces.

United States Patent [191 [111 3,800,673 1 Apr. 2, 1974 Lutz et a1.

[54] WEAR EQUALIZING ARRANGEMENT FOR THE VALVE PLATE OF AN AXIAL PISTON MACHINE [75] Inventors: Gerhard Lutz, Faumdau; Karl Veil,

v Uhingen, both of Germany [73] Assignee: Robert Bosch GmbII, Stuttgart,

Germany [22] Filed: Sept. 11, 1972 [21] Appl. No.: 288,001

[30] Foreign Application Priority Data Sept. 9, 1971 Germany 2145056 [52] US. Cl. 91/487 [58] Field of Search ..'91/485 G, 488

[56] References Cited UNITED STATES PATENTS R20,026 6/1936 Thoma 91/487 1,867,308 7/1932 Durner. 91/487 2,847,938 8/1958 Gowdekm. 91/488 2,972,962 2/1961 Douglas 91/487 3,040,672 6/1962 Fourster et a1.. 91/487 3,232,239. 1/1966 .lonkers et a1 91/499 3,487,788 1/1970 Thoma 91/499 3,669,568 6/1972 McLeod 91/487 FOREIGN PATENTS OR APPLlCATlONS 767,213 1/1957 Great Britain 91/487 9 Primary ExaminerWilliam L. Freeh Attorney, Agent, or FirmMichael S. Striker [57] ABSTRACT In an axial pisto'n machine, the rotary control face of the cylinder block slides on the stationary control face of a valve plate which has a pair of part-circular inlet and outlet slots swept by cylinder ports of the cylinder block. Fluid flowing through the slots and leaking between the control faces, contains impurities so that annular sealing face portions of the stationary control face adjacent the slots, tend to be more worn than the annular supporting face portions located radially inward and radially outward of the sealing face portions. Radial grooves, or grooves slanted in the direction of rotation, connect the slots directly with the outer and- /or inner supporting face portions so that'the impurities produce wear of the supporting face portions, substantially equal to the wear of the sealing face portions, whereby a constant clearance is maintained between the eontrol faces.

10 Claims, 5 Drawing Figures 1 wEAR EQUALIZING ARRANGEMENT FOR THE VALVE PLATE OF AN AXIAL PISTON MACHINE BACKGROUND OF THE INVENTION The present invention relates to an axial piston machine which has a rotary cylinder block containing reciprocating pistons, and having a rotary control face cooperating with a stationary control face of a valve plate which has a pair of part-circular control slots connected with the inlet and outlet of the machine, and being swept by the cylinder ports.

In axial piston pumps of this type, it is necessary to hold the leakage losses between the control faces at a small value, even if the machine operates at pressures up to 300 atm. for a long period of time. Due to the impurities contained in the fluid, such as oil, which enter the clearance gap between the rotary control face of the cylinder block and the stationary control face of the valve plate, the latter is subjected to wear which is greatest at the sealing face portions which are located directly adjacent the control slots. Outward and inward of the sealing face portions, annular. supporting face portions are located, which cooperate with corresponding annular support portions of the rotary control face, and are less worn. Due to this fact, the width of the clearance between the rotary control face and the stationary controlface is uneven, and the width of the gap in. the region of the worn sealing face portions is greater than at the outer and inner annular supporting face portions which are located in the region of the smallest and greatest diameter along which the rotary control face of the cylinder block still abuts the stationary control face of the valve plate. The uneven width of the clearance causes an increase of the leakage, which may result in failure of the pump.

The German DAS 1,142,481 discloses an axial piston machine in which the control face of the valve plate is provided with recesses concentric to the control slots and located outward of the same. Throttle grooves connect the recesses with the control slots so that the pressure fluid in the recesses produces high pressure areas. Furthermore, the impurities carried along by the pressure fluid cause wear in the region of the recesses, similar to the wear of thesealingface portions adjacent the control slots. A uniform wear of the entire stationary control face of the valve plate cannot be obtained by the prior art, since the outer and inner supporting face portions are subjected to lesser wear.

SUMMARY OF THE INVENTION It is one object of the invention to equalize the wear on all face portions of the control face of a valve plate.

Another object of the invention is to control the wear of the control face of the valve plate in such a manner that the width of the clearance between the stationary and rotary control faces remains constant.

Another objectof the invention is to conduct fresh pressure fluid containing impurities from the high pressure control slot directly to a supporting face portion of the stationary control face so that the same is worn off. i

With these objects in view, the present invention provides passages, preferaby grooves, in the stationary control face of the valve plate in accordance with the invention. The grooves are connected at one end with the control slots, and at the other end with the annular supporting face portions located in the region of the greatest and/or smallest diameter of the stationary valve control face which is in contact with the rotary control face of the cylinder block.

In this manner, substantially the same wear is produced on the entire surface of the stationary control face, and irrespective of the wear, the clearance between the rotary control face and the stationary control face remains constant, resulting in a small and constant leakage loss.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an axial sectional view illustrating an axial piston machine in which the invention is embodied;

FIG. 2a is a fragmentary cross-section view taken on line IIaIIa in FIG. 1;

FIG. 2b is a fragmentary sectional view taken on line IIb-Ilb in FIG. 2a;

FIG. 3 is a fragmentary view illustrating a portion of a valve plate in accordance with a modified embodiment of the invention; and

FIG. 4 is a fragmentary view illustrating a portion of a valve plate in accordance with another modification.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An axial piston machine as shown in FIG. 1 has a housing 1 closed by a cover 2. A shaft 3, carrying the cylinder block .4, is mounted in bearings of housing 1, 2 for rotation. Cylinder block 4 has cylinder bores 5 opening in cylinder ports 5a, and containing pistons 7 whose slide shoes 7a slide on a stationary swash plate 6. The other end of cylinder block 4 has a rotary control face 4a in which the cylinder ports 5a open. A spring 8 urges the cylinder block, and more particularly the rotary control face 4a, into sliding engagement with the stationary control face 9 of a valve plate 10 which is secured to housing 2.

Valve plate 10 has part-circular slots 11 and 12, best seen in FIG. 2a, and respectively communicating with inlet and outlet openings 13, 14 in housing 2 so that fluid is supplied through the part-circular slots 11 and 12 to the cylinder ports 5a.

Referring now mainly to FIG. 2a which shows the stationary control face 9 of the stationary valve plate 10,

the two part-circular slots 11 and 12 have ends spaced from each other and located on opposite sides of a plane of symmetry. During passage of the cylinder port 5a from slot 11 to slot 12, the respective cylinder is disconnected from the inlet and connected with the outlet in a dead center position. On opposite sides of the control slots 11 and 12, annular sealing face portions 15 and 16 are formed, on which corresponding face portions of the rotary control face 4a of cylinder block 4 slide. Recesses 17, 18, 19 and 20 are formed in the control face 9 and have a part-circular configuration so that the four recesses 17 to 20 are located along a circle concentric with the axis of rotation of the machine and the center of the control face 9. Ducts 21, 22, 23, 24 connect the recesses 17 to 20 with the interior of housing 1, 2.

Outwardly of the recesses 17 to 20, and of the annular sealing face portion 16, an annular supporting face portion 25 is located which cooperates with the corresponding annular supporting face portion on the control face 4a of the cylinder block 4. Annular control face portion 25 is bounded on the outside by the circular edge of the control plate 10. The rotary control face 4a has the same diameter. The annular sealing face portion 16 is located in the same plane as the annular supporting face portion 25.

Concentric to the annular sealing face portion inwardly spaced from the same, recesses 26, 27, 28, 29 are provided which are connected by passages 30, 31, 32, 33 with the interior of housing 2. Recesses 26 to 29 are located inward of the annular sealing face portion 15, and outward of an inner annular supporting face portion 34.

The control slots 11 and 12 communicate with passages or grooves 35, 36, 37, 38 which project outward in radial direction and have outer ends opening on the annular supporting face portion 25. In the same manner, passages or grooves 39, 40, 41, 42 project inward from the control slots 11 and 12 in radial direction toward the smallest diameter over which the control face 4a of the cylinder block passes, so that the passages or grooves 39 to 42 open on the inner annular face portion 34.

The grooves 35 to 38, and the grooves 39 to 42 have the greatest cross section at the ends communicating with the control slots 1 1 and 12, and the smallest cross section in the region of the inner and outer annular supporting face portions 34 and 25. Preferably, the grooves have a constant width, as shown in the FIG. 2a, and a depth gradually reduced toward the supporting face portions 25 and 34, as best seen in FIG. 2b.

As shown in FIG. 2a, the grooves 35 to 38 and 39 to 42 form pairs in radial direction, and each pair of grooves is spaced an angle of 45'from the plane of symmetry of the control slots 11 and 12 where the dead center of the piston movement is located.

During operation of the machine, cylinder block 4 is pressed by the fluid pressure so that its control face 4a moves away from the control face 9, increasing the clearance or gap between the control faces so that a leakage flow takes place through the clearance, as is required for lubricating and cooling the valve plate 10. The impurities contained in the fluid enter into the clearance and cause substantial wear of the annular sealing face portions 15 and 16.

Due to the fact that the pressure fluid containing impurities can flow through the grooves 35 to 42 to the supporting face portions 25 and 34 of the control face 9, impurities arealso placed between the rotary control face 4a and the supporting face portions 25, 34, which are worn to the same extent as the annular sealing face portions 15 and 16.

Due to the uniform wear of the entire surface of the control face 9, the width of the clearance, and thereby the volume of leakage fluid, remains constant during the span of life of the machine At the same time, the

' pressure fluid flowing through the'grooves 35 to 42, has

a cooling effect on the sealing face portions 15, 16. The pressure fluid entering the recesses 17 to 20 and 26 to 29 flows through the passages 21 to 25 and 30 to 33 into the interior of the housing.

In a simplified construction of the arrangement, the inner supporting face portion 34 can be omitted, together with the recesses 26 to 29 and the grooves 39 to 42.

In the modification illustrated in F IG. 3, the substantially radial grooves 38, 42, for example, are replaced with grooves 48 and 49 which are slanted toward the direction of rotation of the rotary cylinder block. Groove 48 defines in the direction of rotation an acute angle with a tangent at the point where the end of groove 48 communicates with the control slot 46, and the groove 49 is slanted the same acute angle to the tangent at the point where the end of groove 49 communicates with the slot 46. The slanted position of grooves 49 and 48 has the advantagethat during rotation in one direction of the cylinder block 4 a greater volume of pressure fluid with impurities is supplied to the outer and inner annular supporting face portions 47 and 47 so that the wear of these face portions is increased. In the modification shown in FIG. 4, where it is assumed that the inner annular supporting face portion is omitted, and only the outer annular supporting face portion 54 has to be provided with pressure fluid, two slanted grooves 51 and 52 cross each other and project in opposite circumferential directions so that pressure fluid with impurities directly flows through one of the grooves from control slot 43, dependent on the direction of rotation so that the direction of rotation of cylinder block 3 can be reversed, and sufficient pressure fluid flows to the outer annular supporting face portion 54, irrespective of the direction of rotation.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of wear equalizing arrangements for valve plates differing from the types described above.

While the invention has been illustrated and described as embodied in a wear equalizing arrangement for the valve plate of an axial piston pump comprising grooves for supplying pressure fluid with impurities to the outer annular supporting control face portion of the stationary control face of a valve plate, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

We claim:

1. Wear equalizing arrangement for a valve plate of an axial piston machine, comprising a housing having an inlet and an outlet; cylinder block means mounted in said housing for rotation about an axis and having a rotary control face; and valve plate means secured in said housing and having two part-circular slots communicating with said inlet and outlet, respectively, said valve plate having a stationary control face in sliding contact with said rotary control face so that impurities in a fluid leaking from said slot causes greater wear on said annular sealing face portions of said stationary control face located on opposite sides of, and adjacent said slots than on at least one annular supporting face portion of said stationary control face separated in radial direction by one of said sealing face portions from said slots, said valve plate being provided in said stationary control face with grooves extending from said slots through at least one of said sealing face portions and ending distant from said slots at said supporting face portion, each of said gooves being substantially closed by said rotary control face so that fluid containing impurities flows through said grooves to said supporting face portion for increasing the wear thereof to be substantially equal to the wear of said sealing face portions, whereby a clearance of constant width is maintained between said control faces.

2. Arrangement as claimed in claim 1 wherein said grooves extend in substantially radial direction.

3. Arrangement as claimed in claim 1 wherein said grooves have a cross section gradually decreasing from said slots to said supporting face portion.

4. Arrangement as claimed in claim 3 wherein said grooves have a constant width, and a depth gradually decreasing toward said supporting face portion.

5. Arrangement as claimed in claim 1 wherein each of said grooves is slanted to the tangent on the respective part-circular slot at the point where one end of the respective groove communicates with the respective slot so that the direction of said grooves have compo- 6 nents in the direction of rotation of said cylinder block whereby a great volume of fluid enters the other end of said grooves.

6. Arrangement as claimed in claim 5 wherein each slanted groove forms a pair with another groove in said stationary control face slanted in the opposite direction and connecting the respective slot with said supporting face portion whereby fluid flows mainly through one or the other groove depending on the direction of rotation of said cylinder block.

7. Arrangement as claimed in claim 1 wherein said two part-circular slots have ends spaced in circumferential direction, adjacent ends being located on opposite sides of an axial plane of symmetry; and wherein the same number of said grooves is located on opposite sides of said plane of symmetry.

8. Arrangement as claimed in claim 7 wherein said grooves are angularly spaced through angles of substantially 45 from said plane of symmetry.

9. Arrangement as claimed in claim 1 wherein said annular supporting face portion of said stationary control face is located adjacent and radially outward of the radially outer annular sealing face portion of said stationary control face.

10. Arrangement as claimed in claim 9 wherein said stationary control face includes another annular supporting face portion located within the radially inner sealing face portion; and wherein said valve plate means is formed with other grooves connecting said slots with said annular inner supporting face portion for increasing the wear thereof. 

1. Wear equalizing arrangement for a valve plate of an axial piston machine, comprising a housing having an inlet and an outlet; cylinder block means mounted in said housing for rotation about an axis and having a rotary control face; and valve plate means secured in said housing and having two part-circular slots communicating with said inlet and outlet, respectively, said valve plate having a stationary control face in sliding contact with said rotary control face so that impurities in a fluid leaking from said slot causes greater wear on said annular sealing face portions of said stationary control face located on opposite sides of, and adjacent said slots than on at least one annular supporting face portion of said stationary control face separated in radial direction by one of said sealing face portions from said slots, said valve plate being provided in said stationary control face with grooves extending from said slots through at least one of said sealing face portions and ending distant from said slots at said supporting face portion, each of said gooves being substantially closed by said rotary control face so that fluid containing impurities flows through said grooves to said supporting face portion for increasing the wear thereof to be substantially equal tO the wear of said sealing face portions, whereby a clearance of constant width is maintained between said control faces.
 2. Arrangement as claimed in claim 1 wherein said grooves extend in substantially radial direction.
 3. Arrangement as claimed in claim 1 wherein said grooves have a cross section gradually decreasing from said slots to said supporting face portion.
 4. Arrangement as claimed in claim 3 wherein said grooves have a constant width, and a depth gradually decreasing toward said supporting face portion.
 5. Arrangement as claimed in claim 1 wherein each of said grooves is slanted to the tangent on the respective part-circular slot at the point where one end of the respective groove communicates with the respective slot so that the direction of said grooves have components in the direction of rotation of said cylinder block whereby a great volume of fluid enters the other end of said grooves.
 6. Arrangement as claimed in claim 5 wherein each slanted groove forms a pair with another groove in said stationary control face slanted in the opposite direction and connecting the respective slot with said supporting face portion whereby fluid flows mainly through one or the other groove depending on the direction of rotation of said cylinder block.
 7. Arrangement as claimed in claim 1 wherein said two part-circular slots have ends spaced in circumferential direction, adjacent ends being located on opposite sides of an axial plane of symmetry; and wherein the same number of said grooves is located on opposite sides of said plane of symmetry.
 8. Arrangement as claimed in claim 7 wherein said grooves are angularly spaced through angles of substantially 45* from said plane of symmetry.
 9. Arrangement as claimed in claim 1 wherein said annular supporting face portion of said stationary control face is located adjacent and radially outward of the radially outer annular sealing face portion of said stationary control face.
 10. Arrangement as claimed in claim 9 wherein said stationary control face includes another annular supporting face portion located within the radially inner sealing face portion; and wherein said valve plate means is formed with other grooves connecting said slots with said annular inner supporting face portion for increasing the wear thereof. 